1. Field of the Invention
The present invention relates to a power transmission assembly for a vehicle.
2. Related Art
As disclosed by U.S. Pat. No. 8,327,639 B, there is a well-known conventional working vehicle, such as a lawn mower, a skid steer loader, or a track loader, which is equipped with an engine, and right and left traveling devices driven by power of the engine. The driving directions and speeds of the respective right and left traveling devices are individually controlled for turning the vehicle, instead of a steering mechanism. Typical right and left traveling devices use right and left drive wheels or crawlers.
The vehicle is equipped with a power transmission system for transmitting power of the engine to the right and left traveling devices. The power transmission system includes a power distribution unit, right and left fluid duct plates (center sections), right and left hydraulic pumps, right and left hydraulic motors, and right and left speed reduction devices.
Right and left fluid duct plates face each other at respective proximal side surfaces thereof. The power distribution unit is configured between upper portions of the proximal side surfaces of the right and left fluid duct plates. An input shaft of the power distribution unit is extended in the vertical (or fore-and-aft horizontal) direction of the vehicle, and is provided thereon with a pulley for driving connection to a vertical (or fore-and-aft horizontal) engine output shaft of the engine.
The right and left hydraulic pumps are mounted onto the upper portions of the proximal side surfaces of the fluid duct plates so as to have respective pump shafts laterally horizontally extended perpendicular to the proximal side surfaces of the fluid duct plates. The power distribution unit includes a power directive conversion mechanism for transmitting the rotary power of the vertical (or fore-and-aft horizontal) input shaft to the laterally horizontal pump shafts. The power directive conversion mechanism includes a bevel gear fixed on the input shaft, and bevel gears fixed on the respective motor shafts so as to mesh with the bevel gear on the input shaft.
The right and left hydraulic motors are mounted on lower portions of the proximal side surfaces of the respective right and left fluid duct plates so as to be fluidly connected to the respective hydraulic pumps via respective closed fluid circuits formed in the fluid duct plates. Motor shafts of the respective right and left hydraulic motors are laterally horizontally extended perpendicular to the proximal side surface of the fluid duct plates. The right and left speed reduction devices are mounted on lower portions of distal side surfaces of the respective right and left fluid duct plates so as to support respective output shafts drivingly connected to the respective right and left traveling devices. Distal end portions of the motor shafts of the right and left hydraulic motors project distally from the respective fluid duct plates, so that the speed reduction devices drivingly connect the distal end portions of the respective motor shafts to the respective output shafts.
As mentioned above, the power directive conversion mechanism is complicated and expensive because it includes the bevel gears on the input shaft and on the pump shafts, thereby complicating the structure of the power distribution unit, and increasing costs for manufacturing the power distribution unit. Further, the bevel gears serving as the power directive conversion mechanism cause an increase in power loss, thereby increasing fuel costs. Further, the power distribution unit has a large lateral width to have the power directive conversion mechanism so that the vehicle should have a large lateral width.
Further, to constitute the power directive conversion mechanism, the right and left hydraulic pumps are integrated in the power distribution unit. In other words, the lateral width of the power distribution unit defines the span between the right and left fluid duct plates. Therefore, the right and left fluid duct plates are not able to be located freely so as to correspond to another vehicle having a different lateral width or having an engine at a different position.